fix(router): correctly sort route matches with children by specificity

This changes the way we calculate specificity. Instead of using a number,
we use a string, so that combining specificity across parent-child instructions
becomes a matter of concatenating them

Fixes #5848

Closes #6011

modules/angular2/src/facade/lang.dart

@@ -11,6 +11,7 @@ class Math {
   static final _random = new math.Random();
   static int floor(num n) => n.floor();
   static double random() => _random.nextDouble();
+  static num min(num a, num b) => math.min(a, b);
 }
 
 class CONST {